The present invention relates to a method of operating a boiling-water reactor which is and, more particularly, to a method of operating a boiling-water reactor suitable for the second and the following cycles.
Generally, some initial loading fuel assemblies (hereinafter referred to as xe2x80x9cinitial loading fuelsxe2x80x9d) are taken out of the reactor core of a nuclear reactor after the completion of an operation for the first cycle and are replaced with new reload fuel assemblies (hereinafter referred to as xe2x80x9creload fuelsxe2x80x9d). The fuel assemblies taken out of the nuclear reactor have burn-ups which are smaller than those of other fuel assemblies and so they generate a small amount of energy.
A method of operating a nuclear reactor, as disclosed in Japanese Patent Laid-open No. Hei 3-214097, loads at least fuel assemblies taken out of the reactor core of the nuclear reactor after the completion of the second cycle again into the reactor core when exchanging the fuel after the completion of the third cycle to increase the discharge exposure of the initial loading fuels and to reduce the number of reload fuels.
A technique, as disclosed in Japanese Patent Laid-open No. Hei 4-249794, controls the operation of a nuclear reactor by using only control rods adjacent to fuel assemblies not having a minimum enrichment factor and included in initial loading fuels loaded into the initial reactor core by arranging fuel assemblies having large enrichment factors in a peripheral part of the initial reactor core and by arranging fuel assemblies having small enrichment factors in a central part of the initial reactor core to increase the burn-up of the fuel assemblies removed from the reactor core after the completion of the first cycle.
A prior art technique, as disclosed in Japanese Patent Laid-open No. Hei 6-186372, constructs each of the control cells by using four fuel assemblies, including fuel assemblies having large infinite multiplication factors (hereinafter referred to as xe2x80x9clarge-infinite-multiplication fuelsxe2x80x9d), inserts control rods into the control cells in response to a decrease of the infinite multiplication factor of the large-infinite-multiplication-factor fuels below the mean infinite multiplication factor in the reactor core in one cycle, and operates the nuclear reactor in this state for the remaining period of the cycle.
It is mentioned in Japanese Patent Laid-Open No. Hei 6-186372 that many fuel assemblies having small infinite multiplication factors (hereinafter referred to as xe2x80x9csmall-infinite-multiplication-factor fuelsxe2x80x9d) are arranged outside the control cell, and so a sufficiently large number of the small-infinite-multiplication-factor fuel assemblies can be arranged in the outer peripheral region of the reactor core, and hence the reactor core permits only slight neutron leakage. It is also mentioned in this cited reference that the construction of the control cells by assembling the fuel assemblies including small-infinite-multiplication factor fuels and the arrangement of a sufficiently large number of small-infinite-multiplication-factor fuels in the outer peripheral region of the reactor core, as compared with the construction of control cells by assembling only small-infinite-multiplication-factor fuels and the arrangement of an insufficient number of small-infinite-multiplication-factor fuels in the peripheral region of the reactor core, are effective in improving fuel economy.
The prior art technique mentioned in Japanese Patent Laid-open No. Hei 3-214097 loads the initial loading fuels again into the reactor core to increase the burn-up of the initial loading fuels and considers no measures for increasing the burn-up of reload fuels.
The prior art technique mentioned in Japanese Patent Laid-open No. Hei 4-249794 gives no consideration to the second and the following cycles.
The prior art technique mentioned in Japanese Patent Laid-open No. Hei 6-186372 gives no consideration to the reduction of the number of reload fuels.
It is an object of the present invention to provide a method of operating a nuclear reactor, which method is capable of reducing the number of reload fuels to be loaded into the nuclear reactor in the second and the following cycles.
With the foregoing object in view, according to the present invention, a method of operating a nuclear reactor having a reactor core, in which a plurality of reload fuel assemblies respectively having different infinite multiplication factors are arranged, inserts control rods in control cells each comprising four reload fuel assemblies having relatively large infinite multiplication factors among the plurality of reload fuel assemblies for a period longer than half of the period of an operation cycle.
According to the present invention, a method of operating a nuclear reactor having a reactor core, in which a plurality of reload fuel assemblies respectively having different infinite multiplication factors and initial loading fuel assemblies are arranged, inserts control rods in control cells each comprising four reload fuel assemblies having relatively large infinite multiplication factors among the plurality of reload fuel assemblies and the initial loading fuel assemblies in a period longer than half of the period of an operation cycle.
The burn-up of the fuel assemblies forming the control cells into which the control rods are inserted is suppressed by the control action of the control rods. Accordingly, when the nuclear reactor is operated with the control rods inserted into the control cells each comprising large-infinite-multiplication-factor fuels, the fuel assemblies of the control cells have large infinite multiplication factors in the next cycle. Since the fuel assemblies having large infinite multiplication factors can be used in the next cycle, the number of the reload fuels can be reduced by a number equal to the number of those fuel assemblies having large infinite multiplication factors.